audio-talk

Nick · Posted: Thu Jul 29, 2010 8:48 pm Post subject:

A 76 on its own may be a little low in gain, but it could work ok depending on the source.

simon · Posted: Thu Jul 29, 2010 9:37 pm Post subject:

Yep, same old problem. Use one of Steve's old Brit drivers with a gain of 40-odd or 2 stages (26 & 10Y!) for 50+. Half a 6SN7 would be 20ish, but what about a 5751 at 70ish? In an Aikido that would be 35, and would that remove the need for the CF?

Nick · Posted: Thu Jul 29, 2010 10:13 pm Post subject:

simon · Posted: Thu Jul 29, 2010 10:34 pm Post subject:

Working out Aikidos gives me a bit of a headache.

Hmmm, now I'm thinking about it I'm not sure I understand the stacked supply. Maybe there's a bit more to this than first glance. To get the Aikido output at -30V will need a -ve supply rail, and then it starts to get complicated.

What about SRPP with a CF Very Happy

pre65 · Posted: Thu Jul 29, 2010 10:50 pm Post subject:

I'm following this with interest, even if not fully understanding. Wink

DTB seemed to think my first version with the trioded 12GN7 (choke loaded) driver was good.

Nick · Posted: Fri Jul 30, 2010 1:25 am Post subject:

simon · Posted: Fri Jul 30, 2010 10:19 am Post subject:

Nice explanation, don't think I'd have got there by myself. Sounds so obvious! I guess the easiest way is two mains txs and two switches, though maybe not the most domestically acceptable solution. Perhaps if the Aikido used SS rectification and the GM70 used a slow start valve rectifier, a couple of damper diodes maybe?

pre65 · Posted: Fri Jul 30, 2010 10:39 am Post subject:

simon · Posted: Fri Jul 30, 2010 10:52 am Post subject:

Damper diodes have quite a slow start, don't they? How many seconds would you say?

SteveTheShadow · Posted: Fri Jul 30, 2010 11:04 am Post subject:

Hi Simon

Damper diodes start up over about a thirty second period so plenty of time for everything to stabilise before the HT comes up to full voltage.

I have 8 6D22S if you want a couple.
They need Magnoval sockets.

Steve

pre65 · Posted: Fri Jul 30, 2010 11:07 am Post subject:

Yes, 30 seconds, and the HT comes in reasonably gently as well, not all of a sudden.

simon · Posted: Fri Jul 30, 2010 11:14 am Post subject:

30s sounds good. Thanks for the offer Steve, but I have a stash of 6CL3 and 6CJ3 for just such an occassion Wink

SteveTheShadow · Posted: Fri Jul 30, 2010 11:19 am Post subject:

andrew Ivimey · Posted: Wed Aug 25, 2010 4:03 pm Post subject:

For some unaccountable reason I decided I need to make a new HT PSU.

So I cut and drilled and yes, I bled (quite a lot).

This time it was still to be a 400volt trafo into SS bridge, into a pair of 6DS22s just to get that lovely slow rise to HT. This time though I used a 100mfd polyprop to 25Henry choke and a 100mfd poly prop to finish off with.

It works ... and why not.
The amp runs cooler even though the voltage of 520 is the same.
I'm not sure the amp doesn't sound better!

Oh, and I have taken ( last week) out the 22ohm resistors that made up the cathode 'mid-point' - didn't need them as there is no hum and the computer PSUs for the GM70 heaters really do cut the mustard; whatever that means - smashing.

The amp is being driven by Squeezer into Hongker DAC. The amp is driving the aforementioned 'Tannoys' and if I want I can make my ears ring and the windows seem to bend outwards; cracks are appearing in the floor tiles!

I'm off for a bath ... and why not!

cressy · Posted: Wed Aug 25, 2010 4:58 pm Post subject:

interesting about the computer psu's, cos i have 2 salvaged from some old pcs i found in the loft. common mode chokes, allsorts of interesting bits and piecesand they have several 5 and 12vdc 30a outputs. plus a -5 and -12v supply. 300b heater supply anyone? Very Happy

(dont tempt me.......... Very Happy

)